1. Field of the Invention
The present invention relates to a control device for compression ignition operation of an internal combustion engine which is capable of performing a compression ignition operation.
2. Background Art
When the compression ignition operation in which air-fuel mixture supplied to an internal combustion engine is burned by compression ignition (compression self-ignition) is employed, since compression ratio is high, the good mileage can be obtained and relatively stable combustion is achieved even with a lean air-fuel ratio, and in addition, since the combustion temperature is relatively low, the amount of generation of NOx can be reduced.
In order to induce compression ignition, it is necessary to increase the gas temperature in a combustion chamber to a predetermined temperature or higher, and hence an internal EGR utilizing exhaust heat is generally employed.
The internal EGR is implemented by so-called minus overlap control in which an exhaust valve is closed at an early timing during an exhaust stroke, and an intake valve is opened at a delayed timing during an intake stroke.
In other words, part of combustion gas is entrapped in the combustion chamber by closing the exhaust valve at an early timing and opening the intake valve at a delayed timing near the top dead center of the intake stroke, and is mixed with intake air taken during the next cycle as remaining gas (internal EGR gas) to increase the gas temperature and hence induce the compression self-ignition.
Control of self ignition to effect at an optimal timing is generally performed by adiabatic compression by adjusting the temperature of fuel before compression by adjusting the amount of remaining gas through minus overlap control of valve timing (For example, JP-A-10-266878).